Fun with NULL pointers, part 1
Jul 31, 2009, 07:32 (1 Talkback[s])
(Other stories by Jonathan Corbet)
"The TUN/TAP driver provides a virtual network device which
performs packet tunneling; it's useful in a number of situations,
including virtualization, virtual private networks, and more. In
normal usage of the TUN driver, a program will open /dev/net/tun,
then make an ioctl() call to set up the network endpoints. Herbert
Xu recently noticed a problem where a lack of packet accounting
could let a hostile application pin down large amounts of kernel
memory and generally degrade system performance. His solution was a
patch which adds a "pseudo-socket" to the device which can be used
by the kernel's accounting mechanisms. Problem solved, but, as it
turns out, at the cost of adding a more severe problem.
"The TUN device supports the poll() system call. The beginning
of the function implementing this functionality (in 2.6.30) looks
like this:"
Complete Story
Related Stories:
